SrTiO₃ glass ceramics

Abstract

The dielectric properties of the strontium titanate aluminosilicate glass-ceramics described in the previous paper have been investigated over the frequency range of 10 to 1000 kHz and temperature range of −170 to 200° C. The dielectric properties were strongly dependent on the crystallization conditions, which determined the amounts of SrTiO₃ and secondary crystalline phases, and the microstructure of the glass-ceramics. Room temperature values of the dielectric constant and temperature coefficient varied from 13.5 and +125 p.p.m. ° C⁻¹ in uncrystallized glass to 47 and −600 p.p.m. ° C⁻¹, respectively, in glass-ceramics crystallized for 16 h at 1100° C.

Relatively low dielectric losses (tanδ=0.002 at 1 MHz) were observed in uncrystallized glass, and the dielectric losses increased with both frequency and temperature. The dielectric loss at temperatures below −50° C increased upon crystallization of SrTiO₃, while the dielectric loss at ambient temperatures (and above) decreased significantly with the crystallization of hexacelsian SrAl₂Si₂O₃. The crystallization of titania in glass-ceramics with high crystallization temperatures resulted in large low frequency, high temperature losses, due to Maxwell-Wagner-Sillars effects. In most glass and glass-ceramic samples, a temperature-independent increase of dielectric loss was observed over the frequency range of 10 to 1000 kHz from −50 to 200° C; the cause of these increased losses was not determined.

Maxima in both the dielectric constant and loss appeared at low temperatures (below −100° C), and their magnitudes increased, as the crystallization temperature or time was increased. In the early stages of crystallization, the dielectric constant maxima could be explained on the basis of dielectric mixing between perovskite SrTiO₃ and the glassy matrix. However, with higher crystallization temperatures, peaks in the dielectric constant and loss were the result of ferroic effects within the SrTiO₃.